linux-kernel - Re: [RFC][PATCH] mm: stop balance_dirty

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Date:	Thu, 25 Jun 2009 11:10:33 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Richard Kennedy <richard@....demon.co.uk>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] mm: stop balance_dirty_pages doing too much work

On Thu, Jun 25 2009, Peter Zijlstra wrote:
> On Wed, 2009-06-24 at 15:27 -0700, Andrew Morton wrote:
> > On Wed, 24 Jun 2009 11:38:24 +0100
> > Richard Kennedy <richard@....demon.co.uk> wrote:
> > 
> > > When writing to 2 (or more) devices at the same time, stop
> > > balance_dirty_pages moving dirty pages to writeback when it has reached
> > > the bdi threshold. This prevents balance_dirty_pages overshooting its
> > > limits and moving all dirty pages to writeback.     
> > > 
> > >     
> > > Signed-off-by: Richard Kennedy <richard@....demon.co.uk>
> > > ---
> 
> Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>

After doing some integration and update work on the writeback branch, I
threw 2.6.31-rc1, 2.6.31-rc1+patch, 2.6.31-rc1+writeback into the test
mix. The writeback series include this patch as a prep patch. Results
for the mmap write test case:

Kernel          Throughput      usr     sys     ctx     util
--------------------------------------------------------------
vanilla         184MB/sec       19.51%  50.49%  12995   82.88%
vanilla         184MB/sec       19.60%  50.77%  12846   83.47%
vanilla         182MB/sec       19.25%  51.18%  14692   82.76%
vanilla+patch   169MB/sec       18.08%  43.61%   9507   76.38%
vanilla+patch   170MB/sec       18.37%  43.46%  10275   76.62%
vanilla+patch   165MB/sec       17.59%  42.06%  10165   74.39%
writeback       215MB/sec       22.69%  53.23%   4085   92.32%
writeback       214MB/sec       24.31%  52.90%   4495   92.40%
writeback       208MB/sec       23.14%  52.12%   4067   91.68%

To be perfectly clear:

vanilla         2.6.31-rc1 stock
vanilla+patch   2.6.31-rc1 + bdi_thresh patch
writeback       2.6.31-rc1 + bdi_thresh patch + writeback series

This is just a single spindle w/ext4, nothing fancy. I'll do a 3-series
run with the writeback and this patch backed out, to see if it makes a
difference here. I didn't do that initially, since the results were in
the range that I expected.

-- 
Jens Axboe

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